The United States Golf Association (“USGA”) provides five (5) regulations to keep golf balls consistent. Specifically, the golf ball must weight no more than 1.62 ounces and measure no less than 1.68 inches in diameter. The initial velocity of the ball as test on a USGA machine at a set club head speed must not exceed 255 ft/sec. The overall distance of the ball as tested with a USGA specified driver at 160 ft/sec and a 10 degree launch angle must not exceed 296.8 yards. And the ball must pass a USGA administered symmetry test. With these guidelines, one skilled in the art can achieve certain combinations of performance characteristics (such as distance, durability, feel, spin, sound, etc.) through modifications in material compositions, constructions, and surface configurations of various portions of the ball.
Solid core golf balls are well known in the art, which are typically made from polybutadiene rubber materials that, together with high crosslink density, provide the primary source of resiliency for the golf balls. A known drawback of solid cores, such as those based on polybutadiene(s) crosslinked with peroxide and/or zinc diacrylate, is their undesirable sensitivity to and absorption of water vapor and moisture, which reduces core resiliency and degrades other ball properties, such as compression, initial velocity, and coefficient of restitution. Thus, the solid cores are usually encapsulated in a cover to shield them from the invasion of moisture and to maintain optimum ball properties. Conventional cover materials include balata (trans-polyisoprene), ionomer resins, polyurethane, and polyurea, among others. Polyurethane and polyurea covers are generally preferred for their softness, but they exhibit poor moisture barrier properties. Therefore, prolonged exposure to high humidity and elevated temperature poses a particularly significant problem to golf balls of polybutadiene solid core and polyurethane or polyurea cover.
Several prior patents have addressed the water vapor absorption problem. U.S. Pat. No. 5,820,488 discloses a barrier layer having a water vapor transmission rate lower than the cover, formed from polyvinylidene chloride, vermiculite, or a barrier-forming material disposed on the core through an in situ reaction. U.S. Pat. No. 5,875,891 discloses an impermeable packaging that limits moisture absorption by golf balls during storage. U.S. Pat. Nos. 5,885,172 and 6,132,324 disclose thin, hard ionomer-based, inner covers that offer some resistance to water vapor penetration without affecting other ball properties. U.S. Pat. No. 6,232,389 discloses a barrier layer for an air-filled or gas-filled game ball, formed from an aqueous solution of an elastomer, a dispersed exfoliated layered filler, and a surfactant. U.S. Pat. No. 6,398,668 discloses an oxygen barrier layer composed of ethylene vinyl alcohol copolymer.
However, there remains a need for other golf balls with an improved barrier layer and improved methods for applying such a barrier layer in the golf ball.